Brush-supported solar cell washing system and method

ABSTRACT

A method and washer head assembly for washing a surface of a solar panel, includes lowering a washer head frame onto a solar panel. The washer head frame includes a washer frame cross member having a swivel mounted thereon. The swivel is mounted below a center of gravity. The frame includes a upper frame rail and a lower frame rail. A plurality of lath brushes together extend, generally, the length of the washer head frame. The lath brushes are made up to include a plurality of bristles being of sufficient number to support the washer head frame against the surface of the solar panel without damage to the solar panel. The lightness of the frame and the resilience of the brush bristles assure that the washer head frame will not come into damaging contact with the solar panel.

FIELD OF THE INVENTION

The method and system sets forth a means for washing solar cells inarrays and, specifically, the use of brushes to support a washing frameand to dislodge blocking detritus on the surface of the cells.

BACKGROUND OF THE INVENTION

Airborne particles and their accumulation on solar cells are cuttingenergy output by more than 25 percent in certain parts of the world.Atmospheric particulate matter deposited on solar panel surfaces reducessolar energy transmittance actually reaching the photovoltaics. Just asa solar cell in the shade will not produce as much electricity as one indirect intense sunlight, each particle on the surface of the solar cellplaces that part of the cell beneath it in the shade diminishing theoutput of the cell. The more particulate or dust residing on the surfaceof the solar cell, the smaller the area of the cell that is exposed tosunlight and, consequently, the less power that cell produces.

Worldwide solar energy production is expected to increase more rapidlythan any other energy source into the middle of this century, especiallyin regions furthest from hydroelectric resources which, coincidentally,also experience high levels of dust including large areas of India,China, and the Arabian Peninsula. Results indicate that solar energyproduction is currently reduced by ˜17-25% across these regions.Particulate matter is responsible for ˜1 and ˜11 GW of solar powerreduction in India and China, respectively, underscoring the large rolethat particulate matter plays in reducing solar power generation outputwherever it is allowed to rest on solar cell surfaces.

Studies indicate that for solar panel surface cleanings that occur every20-30 days, power generation increases by on average ˜50% after eachcleaning. Past studies have shown that wind-blown dust deposited onsolar panels can influence solar panel performance by decreasing theamount of energy reaching the photovoltaics. But, as in all matterswhere economics must be considered, one must balance the cost ofcleaning against the gains to be enjoyed when the cells have beencleaned.

The current solution for washing photocell arrays have been impaired bythe extremely sophisticated control solutions that are necessary forpositioning washing heads on solar panels. These hydraulic actuatorsmust be controlled to avoid cataclysmic contact with the cell. Thedanger of injury to the solar panels is so great that the controllers ofsuch conventional washers often exploit proximity sensors such as soundwaves to range the solar cell surface. In short, the washing head ismassive and positioned to hover just above the surface of the cell suchthat the scope of a rotating brush's bristles graze the surface whichmotivates dust off of the surface to be rinsed away in a spray of waterand soap in solution.

An example of such a device is described in U.S. Pat. No. 10,305,419issued to Daniel Shugar on 28 May 2019. With the number of sensors andthe massive hydraulic actuators, the center of balance shifts as thehead is moved outward or inward from the carrying vehicle. Such massivedevices are carried on vehicles which must be counter-balanced orstabilized to prevent that mass from upsetting the vehicle and allowingthe head to crash into the solar cell. Solar panels often contain lead,cadmium, and other toxic chemicals that cannot be removed withoutbreaking apart the entire panel. “Approximately 90% of most photovoltaicmodules are made up of glass,” notes San Jose State environmentalstudies professor Dustin Mulvaney. “However, this glass often cannot berecycled as float glass due to impurities. Common problematic impuritiesin glass include plastics, lead, cadmium and antimony.” Researchers withthe Electric Power Research Institute (EPRI) undertook a study for U.S.solar-owning utilities to plan for end-of-life and concluded that solarpanel “disposal in regular landfills [is] not recommended in casemodules break and toxic materials leach into the soil” and so “disposalis potentially a major issue.” So, any collision between the head andsolar cell is an extremely dangerous event and to be avoided.

What is needed in the art is a different type of washing vehicle whereinthe balance of the vehicle is not upset by the deployment of the washinghead.

SUMMARY OF THE INVENTION

A method and washer head assembly for washing a surface of a solar panelincludes lowering a washer head frame onto a solar panel. The washerhead frame includes a washer frame cross member having a swivel mountedthereon. The swivel is mounted below a center of gravity. The frameincludes a upper frame rail and a lower frame rail. A plurality of lathbrushes together extend, generally, the length of the washer head frame.The lath brushes are made up to include a plurality of bristles being ofenough to support the washer head frame against the surface of the solarpanel without damage to the solar panel. The lightness of the frame andthe resilience of the brush bristles assure that the washer head framewill not come into damaging contact with the solar panel.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred and alternative examples of the present invention aredescribed in detail below with reference to the following drawings:

FIG. 1 is a perspective view of an inventive washer head assemblymounted on a host vehicle;

FIG. 2 is a detail of the inventive washer head assembly;

FIG. 3 is a perspective view of the inventive washer head assemblymounted on the host vehicle and including an optional water recoverysystem;

FIG. 4 is a cross-section of a hydrocyclone used to reclaim water fromrecovered sludge collected from the solar panel surface;

FIG. 5 is an embodiment of the cleaning sled which requires no vehiclefor support;

FIG. 6 demonstrates the embodiment of the cleaning sled in use totransit over a gap G in a bank of solar cells;

FIG. 7 depicts the embodiment of the cleaning sled to demonstrate itsquality as a man-portable device for transportation especially in closeenvironments; and

FIGS. 8 and 9 are side views demonstrating the clamping mechanism of theembodiment of the cleaning sled employs enabling the sled in each of a“disengaged” and an “engaged” posture relative to a bank of solar cells.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Distinct from the approach taken by the prior art, rather than toexploit heavy hydraulic actuators and such vast and heavy heads toperform the washing of a surface of a solar array 1, the presentinvention relies upon a lightweight washer head assembly 10. In use, thelighter assembly is sufficiently supported by the bristles of theseveral lath brushes to transit a surface of a solar cell without injuryeither to the solar cell or the supporting structure. These same lathbrushes are used to scrub clean the surface of the solar cells that makeup a solar panel. Because the number and area of the brushes is selectedto distribute the weight of the head over a large region of the surfaceof the solar panels 3 that make up a solar array, no particular part ofthe surface must support a large localized vertical force. In this way,the washer head functions in a manner analogous to snowshoes which workby distributing the weight of the person over a larger area so that theperson's foot does not sink completely into the snow, a quality called“flotation.” In a similar manner, the extreme lightness of the washerhead assembly 10, the inventive pulley system, and the balance impartedby eschewing hydraulics as a means of support of the head assembly,allow the floating head assembly to clean the solar panels 3 withsufficient pressure to dislodge dust while never imparting a localizedpressure to fracture the solar panel 3.

Referring to FIG. 1 , the inventive washer represents two distinctelements, i.e. the washer head assembly 10, and the host vehicleassembly 90, which serves both to transport and position the washer headassembly 10 and to present a platform for all hardware that can beseparated from the washer head assembly 10, while necessary to allow thewasher head assembly 10 to accomplish its purpose of washing the solarpanels 3.

In order to place the washer head assembly 10 in proper context, thediscussion starts at the host vehicle assembly 90. By way of example,any vehicle such as a pickup truck, tractor, utility jeep, or even agolf cart may advantageously be used as the host vehicle 91. There is nospecific requirement such as size or specific equipment apart from theavailability of motive power, either electrical or hydraulic to operatewinches, of which more will be said later. But, it is most importantthat the host vehicle 91 be heavy enough to provide a stable platformfrom which the washer head assembly 10 can extend without its weightoversetting the host vehicle 91.

In the presently preferred embodiment, a 2019 Kubota® RTV-X1100C isselected as a non-limiting exemplary vehicle and belongs to a class ofvehicles known as all-terrain vehicles (ATVs). The ATV has found manyuses in agriculture as a substitute for pick-up trucks, horses, and evenwalking. When first appeared in the United States in the 1970s, theywere promoted and sold as a recreational vehicle designed to provide“thrills” for the rider. Riders soon realized that ATVs are usefulmachines to move through areas not accessible with pick-up trucks,four-wheel drives or other motorized vehicles, and the ATV became apopular hunting vehicle. Because solar panel arrays can be placed onland not otherwise suitable for agriculture, either because of grade orlack of irrigation, a solar cell array 1 may be economically sited onrugged land. For any maintenance operations on such lands, an ATV with acoil spring shock absorber system, an automatic clutch, reverse gear,shaft drive, and a differential with a locking mechanism offers theversatility for all forms of maintenance allowing the ATV to servemultiple roles on the solar farm. The availability of a power take-offmay be desirable for some repair and maintenance tasks. For example,apart from serving as the host vehicle 91, the ATV can serve totransport replacement panels where storms many have damaged a single orseveral panels. A power take-off might optionally serve to power devicesused to elevate and place the panels in maintenance.

While the exemplary ATV enjoys the extreme stability afforded byindependent double A-arm suspension and the surefooted drive beingselectably employed in either 4×2 or 4×4 configuration, one importantfacet of the Kubota® ATV is its dimensions for fitting into aisles thesolar cell array 1 defines. With a length of 122.5 inches or a bit overten feet and a width of just over four feet, the Kubota® can easily fitbetween the rows of panels. With its narrow stance, the ATV can sneakbetween anchoring pillars that make up each row's solar panel supportstructure 4. Exploiting a 1123 cc diesel motor producing 24.8 horsepowerand 50.3 ft-lbs. of torque through a variable hydrostatic transmission,the host vehicle 91 can readily climb while transporting the weight ofthe washer head assembly 10. Four-wheel disc brakes, independent frontsuspension and power steering lifts it easily into the realm of afull-size utility vehicle for ease of handling—and its wide tires and7.5″ ground clearance makes it suitable for tough terrain. The cargobed, large enough to carry a four-foot pallet and strong enough to lift1100 pounds of weight, lifts and dumps via a hydraulic bed-lift systemoperated by a single lever.

Module tilt and selection of row spacing determine the peak power a sitecan produce, as well as how effectively that translates into energy forthe owner. By optimizing module tilt and spacing, system designers canimprove a project's cost structure by over 10%, improving the profitmargins and in some cases making an unattractive project profitable.But, where suitably selected, the aisles between the rows of panels canbe laid out with little or no area given over to accommodate thoseaisles. The aisles might, in the optimal configuration, be arranged toreside in the perennially shaded areas between the rows of solar panels3. In use, the solar panels 3 arranged in a row closer to the sun, causethe casting of a shadow behind the solar panels 3 where the row can besituated without giving up any power-generating area behind the solarpanels 3.

The basic tradeoff is straightforward: for a given area, a systemengineer must determine how many modules to install. One approach is tomaximize the productivity of the modules: set the tilt to maximize thesunlight each module receives, and space them far apart so they don'tshade each other. However, this will leave a lot of empty space on thearea of solar farm and result in a smaller system. The other extreme isto pack the modules closer together and reduce the tilt (and thus, theshading). This results in a much larger peak power capacity, but themodules are less productive individually. Other vehicles can readily beused to maintain the solar farm and to serve as host vehicle to thewasher head assembly 10. For purposes of this discussion, then, an ATVis presumed though not to the exclusion of other vehicles to serve ashost vehicle 91.

As stated above, one objective of the invention is to move as much ofthe hardware effecting the cleaning function off of the washer headassembly 10 and onto the host vehicle 91. To that end, the host vehicle91 is selected to carry one of the heaviest (as opposed to the mostdense) elements necessary in the cleaning task. To understand how thisdensity is an overwhelming factor, one needs only to understand how asmall tank, when filled, can represent a great deal of weight in a waterreservoir 96.

One US gallon of water weighs approximately 8.34 lbs. (simplified in theold saw: “a pint is a pound the whole world round”). If one uses acommonly available elliptical tank (i.e. a tank having an ellipticalcross-section common in agricultural applications), selecting one with a30″ width, a 44″ length, and a 31.3″ height would have a capacity of 110gallons. Such a 110 gallon tank weighs 917.4 pounds. For this reason, adesirable placement of nearly one half ton of weight dictates thecentering of that weight low and between the four wheels. Such aplacement contributes to stability of the host vehicle 91 in moving afull water reservoir 96. Because the water reservoir 96 contains suchwater as is needed to clean the solar panels 3, a communicatingpressurized water line is used to move water from the water reservoir 96to the surface of the solar panel 3. The use of the water will bediscussed with reference to the operation of the washer head assembly 10generally below.

As discussed above, however, the host vehicle 91 serves, not only as theresidence for water, but also as the means of transporting the washerhead assembly 10. In order to clean contiguous solar panels 3, thedesired movement of the washer head assembly 10 relative to the surfaceof the solar panel 3 is in a direction parallel to the surface of thesolar panel 3. Thus, one readily perceives that vehicle motivates thewasher head assembly 10 in a direction parallel to the orientation of arow of solar panels 3 that make up the solar cell array 1. There areonly two positions that place the washing head assembly 10 parallel tothe path of the host vehicle 91 and these are to the right (starboard)and left (port) side. (The maritime terms of orientation are used hereto prevent confusion between movement in a direction either to the leftor to the right and an unambiguous and fixed location relative to thevehicle itself (port side or starboard side)). Because an economical useof the vehicle dictates that each passage through the rows is a cleaningpassage (a reasonable assumption as no one mows their lawn byalternating a cutting pass and then a recovery pass; instead, the “lazymower” assures that each pass is a cutting pass regardless ofdirection). Thus, the meaningful movement of the washer head assembly 10is right from port side and left to starboard side. There is no usefulposition between the port and starboard use positions. Thus, thepreferred connection between the host vehicle 91 and the washer headassembly 10 is one that allows transition from port to starboard orstarboard to port. Ideally, the connection will also provide detents ateach of the port and starboard operation positions as the intermediatepositions are not useful except in transition from one to the other.

There are several solutions that are all within the scope of thisinvention. For example, sockets might be provided for insertion of aframework into either of the port or the starboard side of the vehicleholding the washer head assembly 10 either to extend from the port sideto extend from the starboard side. In use, the driver would, at the endof each row, unfasten the washer head assembly 10 from either the portside or the starboard side and then to install the washer head assembly10 on the opposite side of the host vehicle 91. While this is anembodiment of the invention, it is not the preferred embodiment. Thehost vehicle 91 lends no support to the washer head assembly 10 duringthe transition. It relies upon the driver to carry the washer headassembly 10 from one side to the other.

In the presently preferred embodiment, the transition from port tostarboard or starboard to port is accomplished by rotating the washerhead assembly 10 from port to starboard without disconnecting the washerhead assembly 10 from the host vehicle 91. The rotational movement fromport to starboard or starboard to port is very similar to the rotationof a bicycle fork to steer a bicycle. Throughout the range of movement,the fork must support the weight of the bicycle and the rider. Thus, inthe presently preferred embodiment, the washer head assembly 10 isaffixed to a pivot tube 94 supported by a vehicle having a vehiclebracket assembly 93 comprising a vehicle upper bracket 93 u and avehicle lower bracket 931. To enable rotation, the pivot tube 94 isfloated on a lower bearing 951 and captured on by bearing on an upperbearing 95 u. The pivot tube 94 is free to rotate as required fromstarboard to port and port to starboard.

While not visible in FIG. 1 , some embodiments of the invention includetwo detents that prevent the pivot tube 94 from rotating within thevehicle bracket assembly 93. In one embodiment, the pivot tube 94 isdrilled to define a hole that extends through the pivot tube into andthrough a rod within that connects the vehicle upper bracket 93 u to thevehicle lower bracket 931. A pin, such as a toggle pin, clevis pin,clevis lock pin, push button quick release or other known conventionalpin, is inserted through the defined hole fixing the pivot tube 94relative to the vehicle upper bracket 93 u and the vehicle lower bracket931. As described, this clevis pin arrangement will allow the pivot tube94 to be locked into each of two positions: port and starboard, andremoval of the clevis pin will allow the rotation of the pivot tube 94from the one to the other position.

A similar detent can be employed where the pivot tube includes a pivottube flange and one or the other of the vehicle upper bracket 93 u andthe vehicle lower bracket 931 includes a bracket flange. Holes drilledin the flanges will allow a similar locking arrangement and can bearranged to lock the pivot tube in each of two positions for optimalpositioning of the washer head assembly.

Still other detent systems are available. In one embodiment, catches areplaced that capture the pivot tube 94 and is held in place by thesecatches. Once the washer head frame 13 is in either of the port orstarboard position, the pivot tube 94 is held in that position by theoperation of either of the corresponding port or starboard catch. Oncethe catch holds the swinging gate mast frame 39 in place, the washerhead assembly 10 is fixedly oriented in space allowing the washer headframe 13 to be lowered safely onto the solar panel 3.

In another embodiment, no detent is necessary to prevent rotation.Contact with the solar panel prevents rotation of the pivot tube 94relative to the vehicle bracket assembly 93. The presently preferredembodiment allows a freely rotating pivot tube 94 to mount the washerhead assembly 10 upon the host vehicle 91 at a vehicle bracket assembly93. It is the presently less preferred embodiment wherein the pivot pinprevents rotation of the pivot tube 94 within the vehicle bracketassembly 93. In the preferred embodiment, the bearings 95 u and 951cooperate to support the pivot tube 94 allowing rotation moving thewasher head assembly 10 between port and starboard operating positions.

Moving on to FIG. 2 , the washer head assembly 10 is explored. Forpurposes of this discussion, to locate elements, this description setsout the washer head frame 13 which includes a upper rail 17 and a lowerrail 19 defining upper and lower extreme edges. One of the features ofthe instant invention is that heavier hydraulic actuators are eschewedin favor of the far lighter rigging exploiting cables and blocks to liftand place the washer head assembly 10. In a similar manner, the washerhead frame 13 is constructed as the central structure onto which theoperative elements are attached. In the presently preferred embodiment,aluminum makes up the structure of the washer head frame 13. Todayaluminum alloys and carbon fiber are the most common frame materials forsuch an application, but steel, magnesium or titanium frames might alsoprovide rigid structure without undue weight.

There exist certain factors that will dictate the selection andconstruction methods and dimensions. Such factors include:

-   -   Fatigue: The weakening of a material when subjected to repeated        stress or cyclic loading; and    -   Fatigue life: The number of load cycles required for a material        fail.

As stated, an aluminum frame is presently preferred. An aluminum frameis an affordable embodiment both in terms of ease of manufacture and aprice of material than other alternative embodiments. High qualityalloys are easy to procure and manipulate into a quality washer headframe 13; density is the main advantage of aluminum as a frame material.Given its strength and stiffness, a sufficiently strong frame weighs thesame or less than a steel counterpart. Corrosion resistance is anotherbig advantage of aluminum over steel. Aluminum can be used or stored inadverse conditions even without the benefit of a paint or lacquerfinish. A steel frame requires both a finish and a greater attention topropagation of rust. While the application generally does not subjectthe frame to an extreme stress cycle, fatigue life is a factor in theselection and design. As aluminum flexes and shifts, it fatigues andeventually hits its limit. Good design and sufficient attention assurelonger life.

Another alternate embodiment is a carbon fiber washer head frame 13.Carbon fiber is composite laminate made up of tiny fibers suspended intoa resin. A well-made carbon fiber washer head frame 13 can be builtstiffer, stronger and lighter than an aluminum, steel or titanium.Carbon fiber is nearly half as dense as aluminum and much stronger forthe weight. Carbon fiber is extremely customizable. It can offerdifferent characteristics when carbon tubing is made many plies, orlayers, of fibers that are placed in different orientations. Stiffnessand flexibility can be manipulated on different planes of the same tubeto offer huge advantages over all other materials.

Flexible strength and fatigue life is the biggest disadvantage a carbonfiber washer head frame 13 presents. Carbon fiber is a very rigidmaterial that doesn't like to be flexed and bent. As well, much flexingcauses cracks and fissures in the structure and exposes the individualfibers which aren't so strong by themselves. The failure of the basestructure can cause sudden, catastrophic failure of the washer headframe 13 and with such a failure, possible endangerment of the solarpanel 3 that might underlie the washer head frame 13. Nonetheless,proper engineering may obviate the concerns about fatigue life. Thereare few instances where repeated extreme stresses are applied to thewasher head frame 13.

Because of the widespread availability and the long history of use inindustry, steel is both the most available and its formation techniquesare the best known. Engineering steel frames for lightness is possible,but to achieve the ends of the invention, understanding that if steel isused, care must be taken to remove any surplus material. The washer headframe 13 can be formed of steel tubes which are smaller in diameter thanaluminum. The thinner tubes flex more and allow the washer head frame 13to conform more completely to the surface of the solar panel 3. Fatiguelife of a steel tube is nearly twice that of aluminum, so a steel washerhead frame 13 can last much longer under heavy use. As with aluminum,steel comes in varied qualities, from heavy core steel that has no placein the inventive washer to high-quality steel tubing properly configuredto the end use.

Titanium is twice as dense as aluminum but almost half as dense assteel. Fatigue life and tensile strength are titanium's strong points.Titanium fabrication is more labor intensive than steel, aluminum, orcarbon fiber. Fabrication requires more care and more time to cut andweld in a safe, lasting manor. Titanium can be extruded into long, thintubes that are lighter and stronger than steel. Butted and swaged tubesoffer a lot of customization to place material where such will addressstress and minimize fatigue. Price is the main disadvantage of titanium.The process of extracting the metal is expensive and power intensive.Forming it is also more expensive. But, like aluminum a frame oftitanium resists corrosion, even to a greater extent than aluminum.While each material has its advantages, there is nothing exceptresulting lightness of the formed frame that dictates selection of onematerial over the others. Though, if a frame can be suitably fabricatedfrom any material with sufficient strength and lightness, such a washerhead frame 13 is suitable for ends of the invention.

In operation, the washer head frame 13 rests upon an array of lathbrushes 12. The lath brush 12 is the most common and widely used brushshape and style. A lath brush 12 consists of a rectangular or squareshaped brush back. Lath brushes 12 are versatile rectangular shapedbrushes and can be configured in numerous combinations of brush fill,density and tuft pattern. Other embodiments might be constructed on asynthetic, wood, aluminum or steel core into which tufts of fillmaterial are machine stapled, resin-set or hand wire drawn into thecore.

Lath brushes 12 are, advantageously, configured with varying bristleangles across the brush, and, in some embodiments, with water-fed holes.Lath brush blocks can also be designed and machined with the mountingholes for ease, ready to assemble and attach to the washer head frame13, thereby allowing ready replacement with wear. A lath brush 12 ofsuch a design is the easiest and most cost-effective brush to design andto manufacture. So formed, given the availability of a comprehensiverange of synthetic, natural hair, fiber, bristle or mixed materials andcan be selected to minimize any abrasive damage to the surface of thesolar panel 3.

The lath brushes 12 are also economical. A variety of lath brushes 12may be selected to support and to spread the weight of the entire washerhead assembly 10 across the surface of the solar panel 3, again, so asnot to damage that solar panel 3. The lath brushes 12 are of a design ofthe sort suitable for the wet cleaning of large glass areas such aswindows, mirrors and doors. By way of non-limiting example, lath brushes12 may, alternatively, be founded in an injection-molded polypropylenebrush back to minimize the brush's weight. In one embodiment, such adesign is achieved with structural foam, which is light but retains thebrush's strength and durability. Advantageously as well, lath brushes 12may be manufactured by the most economical means using CNC technologiesas well robotically operated, industrial-brush-making machines.Advantageously, lath brushes 13 are to be had at a relatively smallprice even to the extent of being very readily task-designed.

In the presently preferred embodiment, as illustrated, three lathbrushes 12 extend from the upper rail 17 to the lower rail 19, thelength of the washer head frame 13. These three lath brushes 12 arelocated one on each of the port and starboard extremities and on in thecenter of the frame 13. The washer head frame 13 is designed to bebilateral symmetric which advantageously allows the washer head assembly10 to traverse the surface of the solar panel 3 with equal facility ineither direction. In this illustrated embodiment, two additionalhalf-length lath brushes 12 are positioned immediately beneath acentrally located washer frame cross-member 15. The two half-length lathbrushes 12 are positioned parallel to the full-length brushes therebyorienting them perpendicular to the direction of travel across the solarpanel 3 and positioned to bisect the horizontal distance between each ofthe extreme full-length lath brushes 12 and the center lath brush 12.The purpose of such placement is less to meet the cleaning needs thatthe washer head frame 13 is configured to meet, than to assure that anycontact between the washer head frame 13 and the solar panel 3 issuitably buffered by the presence of additional bristles where thewasher head assembly 10 is least able to absorb impact by rotation aboutthe suspending connection. In short, the additional bristles within thehalf-length lath brushes 12 cooperate with those of the full-length lathbrushes 12 to act as a bumper might on a car to absorb impact withoutpermanent damage to the solar panel 3.

As earlier expressed, a pressurized water line 97 supplies water forwashing to the washer head assembly 10. The water line 97 makes theconnection between the water reservoir 96 to a sprayer manifold 22. Thesprayer manifold 22 is a construction of pipes branching the flow ofwater from the water line 97 to multiple nozzles 28 positioned to spraya flow of water onto the solar panel 3 to rinse accumulated dust fromits surface. The criteria for selecting the nozzles 28 are two-fold: 1)the impact efficiency of spray water, which represents the capabilityfor removing contaminants, and 2) the uniformity of the shape of thewater spray at the nozzle tip, which determines the uniformity ofcleaning performance. According to the data sheets provided by themanufacturer, the impact efficiency of the flat-type nozzle at 50° is10%, whereas those of the full-cone and hollow-cone-type nozzles are <1%and 1%, respectively. The spray shape uniformity is determined by thenozzle type and the designated pressure. The flat-type nozzle displayshigher spray uniformity with a fan shape and is the most widely usedtype of nozzle for cleaning. In addition, it displays a higher impactefficiency than that of the hollow-cone- or full-cone-type nozzle.

The sprayer manifold 22 is rigidly affixed to the washer head frame 13at the upper rail 17 providing both fixation and structure for a watersprayer manifold assembly 20. The water sprayer manifold assemblyincludes, extending from the upper end of the sprayer manifold 22 eachof a port and starboard spray header 24. These headers 24 position thenozzles 28 relative to the washer head frame 13, the washer head frame13 positioning the washer head assembly 10 relative to the solar panel 3in use. Thus, the sprayer headers 24 are designed to position, each, twodistinct nozzles 28, in the presently preferred embodiment but there isnothing in the nature of the invention to dictate more or fewer nozzles28 supported by each of the headers 24. As well, in the presentlypreferred embodiment, the sprayer manifold 22 supplies port andstarboard nozzles 28 through sprayer goosenecks 26 that position and fixnozzles 28 that cover the remainder of a swath configured to cover thewhole of a vertical stripe that precedes on one side, port or starboard,and succeeds on the opposite side the passage of the brushes. In anotherembodiment, the manifold also supplies water holes (not illustrated) inthe brush back of lath brushes 12 in accord with the object of theinvention. The water holes mentioned above allow water to “weep” uponthe surface of the solar panel 3 in use augmenting the flow from thenozzles 28 to assure that the bristles may move across the surface ofthe solar panel 3 thereby to minimize or eliminate scratching thereof inuse.

As stated above, the washer head frame 13 is supported at its washerframe cross-member 15 by a spar assembly 30 at a swivel 31 centrallyaffixed to the washer frame cross-member 15. The spar assembly 30comprises an extendable boom 32 that fastens to the swivel 31 in amanner to allow one degree of freedom, specifically so as to allow thewasher head frame 13 to tilt forward and backward (to pitch) but is heldfixed relative to the remaining degrees of freedom, i.e. disallowingmoving up and down (elevating or heaving); moving left and right(strafing or swaying); moving forward and backward (walking or surging);swiveling left and right (yawing); and pivoting from side to side(rolling). In the illustrated example, the extendable boom 32 is formedto include a boom dogleg 33 to assure a junction with the swivel 31 thatmore closely such that a distal portion of the boom 32 approximates ahorizontal orientation to allow the swivel 31 to hingedly orient thewasher head frame 13 to lie parallel to the surface of the solar panel 3as it resides thereon.

The remainder of the spar assembly 30 includes a sliding mast traveler37 having a boom heel gooseneck 35. The boom heel gooseneck 35duplicates the single degree of feed the swivel 31 allows, specificallyto allow the boom 32 to tilt forward and backward (to pitch). Thesliding mast traveler 37 is also configured to travel vertically on aswinging gate mast frame 39. It is the swinging gate mast frame 39 thatis affixed to the pivot tube to allow a single degree of freedom. Inthis case, the pivot tube moves by swiveling left and right (yawing),i.e. the pivot tube is allowed to transit from the port side operatingposition to the starboard side operating position or from that of thestarboard side to that of the port side as has been described aboverelative to the pivot tube 94. The spar assembly 30 serves as the rigidmembers of a derrick-like member for placing the washer head frame 13with the bristles of its several lath brushes 12 to rest on the surfaceof the solar panel 3. The specific actions of this spar assembly 30 aredescribed below in detail relative to motivating rigging and winches.

It is the rigging and winches that accomplish articulation andtranslation of the rigid members of the spar assembly 30 in order tomove the washer head assembly 10 relative to the host vehicle 91. Threewinches are responsible for drawing or settling the above describedextendable boom 32, the sliding mast traveler 37, and for controllingthe yaw of the washer head frame 13. Beginning with the sliding masttraveler 37, a traveler halyard winch 41, draws a traveler halyard 43downward through a traveler halyard sheave 45 rotates within a mastcrosstree 36 mounted uppermost on the swinging gate mast frame 39 suchthat the traveler halyard 43 draws the sliding mast traveler 37 upwardand with it lifting the boom heel gooseneck 35. To lower the boom heelgooseneck 35, the traveler halyard winch 41 pays out the travelerhalyard 43. In such a case, gravity draws the sliding mast traveler 37downward which draws the traveler halyard 43 through the travelerhalyard sheave 45 in the opposite direction as lifting. As such, themovement of the sliding mast traveler 37 likewise translates the washerhead frame 13 upward and downward relative to the host vehicle 91.

As expressed above, the boom heel gooseneck 35 pivotally connects theextendable boom 32 to the sliding mast traveler 37. A boom winch 51mounted on the traveler 37, achieves articulation of the boom 32relative to the traveler 37. The boom winch 51 draws a boom pendant 53through a boom pendant sheave 55. The boom pendant 53 is affixed to theboom 32 by means of a boom crank 57 such that drawing the boom pendant53 draws the boom 32 to rotate upward about the boom heel gooseneck 35.Paying out the boom pendant 53 allows gravity to draw the boom 32downward, rotating about the boom heel gooseneck 35. Optionally, a boompendant drawbar spring 59 is used to buffer the actions of the boompendant 53 as it accelerates and decelerates the movement of the boom 32and, necessarily, the washer head frame 13. Even the lighter mass of theinventive washer head frame 13 still must overcome inertia and dousemomentum as the boom 32 is rotated. Physics will not be denied.

A special type of extension spring, known as a drawbar spring, has asolid stop. A drawbar spring is essentially a compression spring withspecial hooks. In a drawbar spring, the load is applied at the ends oflong steel loops which pass through the spring's center and are hookedaround the opposite end, thus compressing the spring upon loading. Asthe loops are extended one from the other, the hooks compress the springuntil, at the end of the range, the coils of the spring bear againsteach other to stop further movement in that direction. When fullycompressed, the spring acts as a link in a chain until the loops canmove back together relaxing the compressed spring. These springs do notfail upon overloading. Drawbar springs are excellent for use inpotential overload situations and offer a built-in safety feature that,upon fracturing, will continue to carry a static load.

Thus, when, optionally, used to buffer the movement of the boom 32 byusing the boom winch 51 by hauling in or paying out of the boom pendant53, the boom pendant drawbar spring 59 inhibits sudden movement of theboom 32 that might cause impact with the solar panel 3. Because thebristles of the lath brushes 12 also serve as bumpers to spread impactforces the washer head frame 13 imparts when making contact with thesolar panel, the boom drawbar spring 59 serves to further cushion thatimpact by taking up tension as the bristles of the lath brush 12 come torest and, by flexure, begin to exert support for the washer head frame13 against the solar panel 3. The length and resiliency of the lathbrush 12 bristles provides a continuum from just making contact to fullsupport. With the boom drawbar spring 59 also exerting a tensioning uponthe boom pendant 53, the length of the boom pendant 53 paid out ismaximized during that transition.

Moving, then, from the boom pendant 53, the attitude of the washer headframe 13 is controlled, in part, by a jib pendant 63. As stated above,the extendable boom 32 fastens to the swivel 31 in a manner to allow onedegree of freedom, specifically to allow the washer head frame 13 totilt forward and backward (to pitch) but is held fixed relative to theremaining degrees of freedom. So, a jib pendant 63 extends from a jibwinch 61, In the presently preferred embodiment, the jib winch 61 ismounted on the boom 32. The opposite end of the jib pendant 63 isaffixed to the washer head frame 13 above the swivel 31 such thatdrawing in the jib pendant 63 draws the washer head frame 13 to a pitchthat approaches vertical. Because the swivel 31 is located below thewasher head frame 13 center of gravity, paying out the jib pendant 63,from the jib winch 61 allows the washer head frame 13 to approach apitch nearer to horizontal.

Because the swinging gate mast frame 39 is positioned to beperpendicular to the horizontal edge of the solar panel 3, the jib winch61 can be employed to orient the washer head frame 13 to a parallelorientation to the solar panel 3. In that parallel orientation, thewasher head frame 13 is lowered to the solar panel by paying out theboom pendant 53 as described above. By coordinating the operations ofthe jib winch 61 and boom winch 51, the washer head frame 13 can belanded on the solar panel 3 with minimal impact. Once the washer headframe 13 has made contact, both of the jib pendant 63 and the boompendant 53 are allowed to go slack, each with a slight excess so that nopressure can be exerted on the solar panel in movement across thesurface allowing the slight pitching in the washer head frame 13 shouldany be necessary to conform with the surface of the solar panels 3 inthe washer head frame's 13 transit across the solar panels 3.

Once the washer head frame 13 rests upon the solar panels 3, waterissues from the nozzles 28 as pumped from the water reservoir 96 througha pump (not shown). The host vehicle 91 moves down defined aislesparallel to the solar panels 3 as they are arranged in rows. As thevehicle moves forward, the same bristles on the lath brushes 12 now bothsupport washer head frame 13 and scrub the solar panels. The spray ofthe water through the nozzles 28 that strikes the solar panels 3 aheadof the lath brushes 12 loosens dust and provides water to lubricate theindividual bristles prevent scratching the solar panels 3 in theirmovement over the surface. As the dust is loosened by the scrubbingaction of the bristles as the lath brushes 12 pass over the solar panels3. Finally, water issuing from the trailing nozzles 28 rinses theloosened dust from the solar panels so that it may run off the surfacethereby cleaning the solar panel 3.

Referring now to FIG. 3 , it is worthwhile to trace the path of suchwater through the inventive solar panel washer. As shown, a vented waterreservoir 96 resides on the cargo deck of the host vehicle 91. While notshown, a pump draws water from the water reservoir 96 to pressurizewater in a water line 97 to supply the washer head assembly 10 where thewater line 97 joins a sprayer manifold 22 which distributes water amonga pair of spray goosenecks 26 which supply pressurized water forspraying through nozzles 28 mounted on each and a spray header 24 whichsupplies, in this embodiment, another four nozzles 28. Acting inconcert, then, the six nozzles 28 spray water to completely wet each oftwo roughly rectangular bands, each being sprayed by three nozzles 28.One of the two bands immediately precedes the washer head frame 13 andits lath brushes 12 and one immediately follows the washer head frame13. As described above, the host vehicle 91 propels the washer headframe 13 to scrub the solar panels as the nozzles 28 spraying thepreceding band wets the solar panel 3 and dust accumulated thereon, thewasher head frame 13 to scrub the now wetted surface of the solar panel3 and then the nozzles 28 spraying the following band rinse thenow-loosened dust from the surface of the solar panel 3.

In many instances, the embodiment of the invention shown in FIG. 1 iswasteful of water in places where solar panels are advantageouslylocated by the strength of the sun striking the earth in that location.For instance, in desert locations, water might be extremely valuable forirrigation purposes and the getting of a volume of water sufficient toclean the solar panels with the embodiment depicted in FIG. 1 might beprohibitive. For that reason, the alternate embodiment optionallyincludes a water recovery tray 71 to catch such water as might berecovered from the spraying and to separate that water from theentrained dust.

In the embodiment set out in FIG. 3 , all of the elements set out inFIGS. 1 and 2 are present. Further, a water recovery tray 71 dependsfrom the swinging gate mast frame 39 by means of a water recovery traybracket 73. In the presently preferred embodiment, to aid in thestability of the host vehicle 91 with the washer head assembly 10, it isextremely advantageous to remove the water and, hence, its weight, fromthe water recovery tray 71. So, in operation, a water recovery pump 77draws what water collects in the water recovery tray 71 from the tray 71and pumps it through a water recovery return line 75. In such presentlypreferred embodiment, there is a screen that protects the pump from suchgrit and non-dust debris as may have rested on the solar panel 3. Forexample, bird excrement may contain grit, undigested seeds and husks. Abird swallows small bits of gravel that act as ‘teeth’ in the gizzard,breaking down hard food such as seeds and thus helping digestion. Thesestones are called gizzard stones or gastroliths and usually become roundand smooth from the polishing action in the animal's stomach. When toosmooth to do their required work, they may be excreted or regurgitated.Among other debris, should these gastroliths be impelled into the pumpimpeller, the hardness of the gastroliths will greatly accelerate thewear of the pump 77. For that reason, though not shown, the tray 71, ina preferred embodiment, with include a screen or grid to strain thesegastroliths and other debris, thereby protecting the pump 77. But, evenafter straining, the water will still entrain the dust that wasdeposited on the solar panels 3.

The water recovery pump 77 motivates the water recovered from the waterrecovery tray 71 through the water recovery return line 75 to ahydrocyclone 80 to remove all of the dust while harvesting the water forreuse by return to the vented water reservoir 96. Because the washing ofsolar panels does not require that water be returned or, even,conditioned as potable water, it needs only to be relatively in a statefree from corrosive chemicals and dust or debris so as to protect thesolar panel 3 which it washes. In fact, in some embodiments, the waterrecovery return line 75 may be used to draw washing water from standingsurface water from ponds or lakes for washing. The pump 77 enables suchcollection. But, in the presently preferred embodiment, a hydrocyclone80 proves to be very usable to remove dust from the retrieved water,exploiting the kinetic energy the pump 77 imparts to the retrievedwater.

FIG. 4 shows an exemplary hydrocyclone 80 and demonstrates itscentrifugal separation principle to remove dust solids suspended inrecovered water. The operating principle of the hydrocyclone 80 reliesupon a conical vortex-generating cavity 81. Water with suspended dustenters a tangential feed inlet 82 at the top of the cavity 81 wall ofthe hydrocyclone 80. The tangent t proves to the most efficientdirection to exploit most efficiently the kinetic energy motivating thepumped water as it enters the cavity 81. The separated water exits inthe cavity 81 through a vortex finder 87 which further enhances thetangential flow and therefore creates both a strong outer vortex 84traveling downward within the hydrocyclone 80 and an inner vortex 85 ofwater. The water and dust within the hydrocyclone 80 spins in the highvelocity outer vortex 84. As the water flow 88 exits out by the vortexfinder 87 (the overflow), the coarse particles simultaneously spiraloutward, separated by centrifugal force then to fall through theunderflow collect under gravity's influence at the narrow vortex base,the restricted mud port 86. The pressure the outer vortex 84 exerts onthe collected particles urges the particles as very much dewatered mudfrom the restricted mud port 86 in a mud flow 89.

In use, the hydrocyclone's 80 axis a is aligned vertically so gravitywill assist in the removal of dust solids as a mud flow 89. Theoperating principle is simple: the fluid, carrying the suspendedparticles, enters the cyclone tangentially t by the tangential feedinlet 82. Because the particles in suspension are drawn outward as theflow spirals downward, that circular motion produces a centrifugal fieldin an outer vortex 84 drawing particles out of the suspension. Largerparticles move through the fluid to the outside of the cyclone cavity 81in a spiral motion, and, thus, to exit through the restricted mud port86 or spigot with a fraction of the liquid to form a mud flow 89. Due tothe limiting area of the restricted mud port 86 or spigot, an innervortex 85, rotating in the same direction as the outer vortex 84 butflowing upward, is established and leaves the hydrocyclone 80 throughthe vortex finder 87, carrying most of the liquid and some small finerparticles with it.

The outlet at the top of the cavity 81 is called the vortex finder 87and extends into the hydrocyclone 80 to reduce short-circuit flowdirectly from the tangential feed inlet 82. At the conical end of thecavity 81 lies the restricted mud port 86 or spigot. For sizeseparation, both outlets are generally open to the atmosphere. Exceptfor the immediate region of the tangential inlet, the fluid motionwithin the hydrocyclone 80 has radial symmetry. If one or both of theoutlets are open to the atmosphere, a low-pressure zone causes a gascore along the vertical hydrocyclone axis a, inside the inner vortex 85.Water from the vortex finder 87 flows into the water reservoir 96 forreuse in washing.

Rooftop Sled Embodiment

Google conducted a groundbreaking experiment at their 1.6 MW solar farmin Mountain View, California. They found that cleaning the solar panelswas “the number one way to maximize the energy they produce.” Cleaningsolar panels that had been in operation for 15 months doubled theiroutput of electricity.

There are multiple reasons why rooftop solar panels increase fallhazards. One reason is that installing and maintaining rooftop solarpanels means that workers are simply on the roof more often. Whenworkers install rooftop solar panels, they are at risk of dangerousslips, trips, and falls. Installation of rooftop solar panels also meansthat there is less walking area around potential fall areas such asskylights and roof hatches. With less space to maneuver, there is dangerof falls. With equipment and power lines, there are more trip hazards aswell.

Between 2008 and 2014, rooftop solar grew an average of more than 50%per year (U.S. Energy Information Administration (EIA). 2015. MonthlyUpdate May 2015) and continues to grow. But rooftop solar panel systeminstallation and maintenance present potential fall hazards for workers.Because of rooftop fall hazards, the foremost concern in cleaning thepanels is to use proactive measures to prevent a fall. Because the areaof the solar panel is proportionate to the output of the panel, mostinstallations will be designed to maximize the area relative to theperimeter of the roof upon which the panels are installed. Thus, thearea of the roof reserved for the worker is generally minimal relativeto that proportion of the area of the roof dedicated to support thepanels.

Falls from heights is a leading cause of death to workers, accountingfor more than one-third of U.S. construction deaths. In general, theentire rooftop environment dictates a number of safety measures be putin place to prevent falls and fatalities. Roof edges, skylights, androof hatches near rooftop solar panel arrays each present fall hazardsto workers tasked with installation and maintenance. So, there is alegitimate concern about solar panel installation safety for workers onrooftops. FIGS. 5 through 8 depict an embodiment for cleaning of rooftopsolar arrays with a man-portable cleaning sled for such environments.

FIG. 5 introduces an embodiment of the cleaning sled which requires novehicle for support of the brushes over the solar panels. This is aman-portable unit which may be used in any environment but isparticularly well-suited for cleaning rooftop solar panel arrays withtheir narrow passageways between rows of arrays.

FIG. 5 is offered to show some of the features unique to the embodiment.Principal among these distinctions from the previously describedembodiment is the reliance upon the user 2 to motivate the sled acrossthe rows of the solar panel array 1. Rather than relying upon the hostvehicle 91 of the first described embodiment, the sled relies upon theuser 2 pulling the sled by its high-pressure hose 97 as the sledtransits the row of panels 3.

The sled embodiment rolls over the solar panels 3 on trolley suspensionwheels 85, while the lath brushes 12 cooperate to suspend the sled. Thetrolley suspension wheels 85 are ganged in each of an upper trolleyassembly 80 and a lower trolley assembly 82. The sled is positioned overthe panel 3 by each of gangs of lower lateral trolley wheels 83 (in thelower trolley assembly 82) and the upper lateral trolley wheels 81 (inthe upper trolley assembly 80).

The sled itself relies upon a framework comprising a pair of parallelwasher head frames 13 separated by a upper rail 17 and a lower rail 19.The washer head frames 13 also secure the lath brushes 12 to the sled.These lath brushes 12, because of the resilience of the individualbristles do also serve to help to support the sled as the sled rests onthe solar panels 3. As with any brush, the lath brushes 12 do rely upona downward force, in this case exerted by gravity, to scrub dustparticles from the surface of solar panels 3. Given the light weight ofthe sled and the length of the lath brushes 12, the weight of the sledis never focused enough at any one spot to pose any danger to the solarpanels 3.

Water enters the sled through the same high-pressure hose 97 and downthrough the gooseneck 26 to feed a sprayer manifold 22. In turn, thesprayer manifold 22 divides the flow of water, distributing it to eachof a plurality of spray headers 24 which, also in turn, feed water tothe several nozzles 28 to spray onto the surface of the solar panels 3just as described above relative to the first-described embodiment.

To assure the tracking of the sled over the solar panels 3, a backbone18 is a part of the clamping assembly which selectively engages anddisengages the sled from the solar panels 3. The clamping mechanism isdisclosed more fully with reference to FIG. 8 below. Nonetheless, it ismentioned here for completeness of the sled assembly as the clampingmechanism exerts a constant pressure to capture the sled in optimalregistration with the solar panels 3. Also included for laterexplanation are truck wheels 87, which will be set forth relative toFIG. 7 below.

FIG. 6 demonstrates the embodiment of the cleaning sled in use totransit over a gap G in a bank of solar cells having all the sameelements visible as in the preceding FIG. 5 . FIG. 6 differs from FIG. 5in that FIG. 6 depicts the described sled embodiment as it makes thetransit from a first solar panel 3 to a second solar panel 3 across agap G between the panels 3. Each of the upper trolley assembly 80 andthe lower trolley assembly 82 comprise a plurality of trolley suspensionwheels as well lateral trolley wheels, a plurality of lower lateraltrolley wheels 83 in the lower trolley assembly 82 and a plurality ofupper lateral trolley wheels 81 in the upper trolley assembly 80.

The spacing of these wheels 81, 83, and 85 is such as to have at leastthree of each type remain in contact with the two solar panels 3 tomaintain the alignment of the trolley assemblies 80, 82 with panels 3thereby to allow the ready transition from one solar panel 3 to the nextsolar panel 3. Thus, when the user 2 draws the sled by the high-pressurehose 97 from the first solar panel 3, the first of two trolleysuspension wheels 85 (one each from the upper trolley assembly 82 andthe lower trolley assembly 80) as well as one each of the upper lateraltrolley wheel 81 and lower lateral trolley wheel 83, as these fourwheels 81, 83, and 85 enter the gap G, leaving the surface and upper andlower edges of the solar panel 3 simultaneously.

As the user 2 continues to draw the sled along, each of these firstgroup of four wheels 81, 83, and 85 contacts the next solar panel 3 justas a second group of four wheels 81, 83, and 85 leaves the surface andupper and lower edges of the first solar panel. Because at least six ofthe two trolley suspension wheels 85 and three each of the lower lateraltrolley wheels 83 and the upper lateral trolley wheels 81 maintain theupper trolley assembly 80 and the lower trolley assembly 82 in alignmentboth with the surface and edges of the solar panels 3 making a smoothtransition across the gap G to ensure a smooth transition withoutimpediment to the forward movement of the sled.

FIG. 7 shows the embodiment of the cleaning sled to demonstrate itsquality as a man-portable device for transportation especially in closeenvironments. FIG. 7 is actually not complete in that at least four ofthe suspension wheels 85, two of the upper lateral trolley wheels 81 andtwo of the lower trolley wheels 83 have been omitted to allow forgreater clarity relative to the pivoting upper trolley assembly 80 andthe truck wheels 87 on the lower trolley assembly 82. This omission ofthe detail is not intended suggest that the absence of these wheels isintended for the presently preferred embodiment of the sled embodimentof the invention. The principal purpose of FIG. 7 is to demonstrate theplacement and to explain use of the truck wheels.

As stated, the use of the truck wheels assists a user 2 in maneuveringthe sled embodiment especially in close quarters. When tipped up, thesled may be balanced on its pair of truck wheels 87. A class 3 lever hasthe effort between the fulcrum and the load. Because the load and effortare on the same side, they move in the same direction. In a class 3lever, the effort is always closer to the fulcrum than the load, soclass 3 levers are used to make the load move faster.

The wheels act as a fulcrum that helps distribute and mitigate heavyweight on one side. This lever design makes it easier for the user 2 topush and move heavy, large objects with ease. Once on end, the sled isreadily and easily moved through narrow passages. Because the sled isrelatively light, the sled itself can be steered by shifting the wholeof the weight to one of either of the truck wheels 87 and pivot the sledon that one of the truck wheels 87. Once it is aligned with the intendedpath, the user 3 can drop the remainder of the weight back on theremaining truck wheel 87. In such a manner, the sled may be moved inconstricted spaces readily.

FIGS. 8 and 9 depict the clamping mechanism of the embodiment of thecleaning sled enabling the sled to engage a bank of solar cells in eachof an “engaged” position and a “disengaged” position relative to thesolar cells. As stated above, the trolley suspension wheels 85 areganged in each of an upper trolley assembly 80 and a lower trolleyassembly 82. The sled is positioned over the solar panel 3 by each ofgangs of lower lateral trolley wheels 83 (in the lower trolley assembly82) and the upper lateral trolley wheels 81 (in the upper trolleyassembly 80).

A clamping mechanism includes an axial swivel allowing the upper trolleyassembly 80 to rotate from a position wherein the upper lateral trolleywheels 81 contact an upper surface of solar panels 3 to maintain thewasher head frame 13 in alignment to the solar panel 3 in an engagedposition. This same engaged position is characterized, as well, by thepositioning of suspension wheels 85 to roll across a surface of the samesolar panel 3. The upper trolley assembly 80 can also rotate about theaxis of the upper trolley assembly 80 to draw the upper lateral trolleywheels 81 out of engagement with the upper surface of the solar panel 3.As the upper lateral trolley assembly 80 rotates out of engagement withthe solar panel 3, the suspension wheels 85 withdraw from engagementfrom the surface of the solar cell 3 in the disengaged position. Theclamping mechanism comprises a backbone 18 coupled to a cam handle 46and a cam swivel 48 which, in operation, rotate about a cam pivot 47.The cam handle 46, and the backbone swivel 48 are maintained in parallelrelationship by their coupling with each of the backbone 18 and thewasher head frame 13. Movement of the cam handle 46 as depicted in FIG.8 , and its parallel counterpart, the backbone swivel 49 serves to movethe upper trolley assembly 80 to a position of engagement wherein thetrolley suspension wheels 85 and the upper lateral trolley wheels 81 asdepicted in FIG. 9 . A resilient spring 14 spans from the backbone 18 tothe backbone swivel 49 to apply tension tending to draw the uppertrolley assembly 80 into engagement with the solar panel 3.

Cam levers (often called cam clamps) are quick-action fastening devicesallowing the user to quickly release a workpiece without the use oftools or equipment. Once the lever is threaded onto the application,clamping force is applied by pushing down the lever. Clamping force isreleased simply by pressing the cam handle and cam lever into the“disengaged” position as depicted in FIG. 8 , allowing the sled to beremoved from the surface of the solar panel 3. The cam handle 46, whenmoved to the “engaged” position, as depicted in FIG. 9 , as drawn by theresilient spring 14 places the several suspension wheels 85 of the uppertrolley assembly 80 onto the surface of the solar panel 3 where thesuspension wheels 85 and the lath brushes 12 maintain the spacingbetween the washer head frame 13 thereby allowing the lath brushes 12 toscrub the surface of the solar panel 3 when the upper trolley assembly80 is in its “engaged” position as depicted in FIG. 9 .

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:
 1. A washer head assemblyfor washing a surface of a solar panel comprising: a washer head frameincluding: a washer frame cross member including: each of: an uppertrolley assembly, comprising an upper plurality of suspension wheels anda plurality of upper lateral trolley wheels, and a lower trolleyassembly, comprising a lower plurality of suspension wheels and aplurality of lower lateral trolley wheels, the upper trolley assemblyand the lower trolley assembly held in parallel relationship one toanother by a plurality of washer head frames connected thereto; andaffixed on each washer head frame, a lath brush, the lath brushextending, generally, the length of the washer head frame, each lathbrush to include a plurality of bristles to support the washer headframe against the surface of the solar panel without damage to the solarpanel; and a water sprayer manifold assembly, comprising: a plurality ofspray headers, each spray header including at least one spray nozzle; asprayer manifold defining an interior passage to communicate water toeach of the plurality of spray headers and through each spray header tothe at least one spray nozzle the spray header includes; a gooseneck forconnecting a high-pressure hose for communicating a volume of water intothe interior passage of the water sprayer manifold.
 2. The washer headassembly of claim 1 further comprising: a pressurized water line toconvey water to the sprayer manifold, the water-line being configured todraw the washer head assembly across a row of solar panels.
 3. Thewasher head assembly of claim 1, wherein: the upper trolley assemblyincludes an axial pivot allowing the upper trolley assembly to rotateaxially to, alternately, engage or disengage the plurality of upperlateral trolley wheels with the solar panel.
 4. The washer head assemblyof claim 3 wherein the axial pivot is further configured: to engage anddisengage the plurality of upper lateral trolley wheels as the uppertrolley assembly is rotated to engage the upper lateral trolley wheelswith the solar panel in response to movement of a cam lever assembly. 5.The washer head assembly of claim 3 further comprising: the cam leverassembly comprising a cam handle, a cam swivel and a backbone swivelcooperating to rotate the upper trolley assembly to alternately engageor to disengage the upper lateral trolley wheels with the solar panel inresponse to movement of the cam handle.
 6. The washer head assembly ofclaim 5 further comprising: a spring arranged to urge cam lever assemblyso as to rotate the upper trolley assembly to engage the upper lateraltrolley wheels with the solar panel.
 7. The washer head assembly ofclaim 1 further comprising: a plurality of truck wheels rotatablyfastened to the washer head frame, the plurality of truck wheels beingarranged to support the washer head frame when the washer head frame isoriented to a generally orthogonal orientation to a ground surface, thetruck wheels being configured to transport the washer head assembly overthe ground surface.
 8. A method for cleaning a solar panel comprising:suspending a washer head assembly on bristles of a plurality of lathbrushes the washer head frame includes, the lath brushes being held in agenerally parallel orientation by a washer head frame, the lath brushesextending from an upper trolley assembly to a lower trolley assembly;orienting the washer head assembly relative to the solar cell by urginga plurality of upper lateral trolley wheels rotatably fastened to theupper trolley assembly to bear against an upper edge of the solar cell;conveying water in a pressurized water line to supply a water sprayermanifold assembly the washer head frame supports; distributing waterthrough the water sprayer manifold assembly to each of a plurality ofnozzles directed at the solar cell through at least one spray header;and drawing the washer head frame along a path parallel to an axis ofthe upper trolley assembly.
 9. The method of claim 8, further wherein:drawing the washer head frame includes drawing the pressurized waterline to motivate the washer head frame.
 10. The method of claim 8further wherein: orienting the washer head assembly relative to thesolar cell includes by urging a plurality of lower lateral trolleywheels rotatably fastened in a lower trolley assembly, the lower trolleyassembly being connected to the washer head frame against a lower edgeof the solar cell which in concert with the urging of the upper lateraltrolley wheels clamps the washer head frame in orientation to the solarcell.
 11. The method of claim 8 further comprising: suspending a washerhead assembly on bristles of a plurality of lath brushes includes:rotating the washer head frame to a position generally parallel to afront surface of the solar panel and resting on the bristles of theplurality of lath brushes from an initial position resting on aplurality of truck wheels rotatably fastened to the washer head framesuch that in the initial position the plurality of truck wheels supportthe washer head frame in an attitude of generally orthogonal orientationto a ground surface; and resting the washer head frame against the frontsurface of the solar panel such that the bristles of the plurality oflath brushes contact the solar panel front surface.
 12. The method ofclaim 8 further wherein: conveying water in a pressurized water line tosupply a water sprayer manifold assembly includes conveying waterthrough a flexible hose.
 13. The method of claim 12 further wherein:drawing the washer head frame along a path parallel to an axis of theupper trolley assembly includes drawing the washer head frame by pullingthe washer head frame by the flexible hose.
 14. The method of claim 8wherein: drawing the washer head frame along a path parallel to an axisof the upper trolley assembly includes drawing the washer head framewherein from a first position suspended by suspension wheels resting ona first solar panel to a position to a second position such that thesuspension wheels resting on a second solar panel separated from thefirst solar panel by a gap.
 15. A washer head frame for washing asurface of a solar panel, the washer head frame comprising: a pluralityof lath brushes, the plurality of lath brushes together extending,generally, the length of the washer head frame, each lath brush makingup the plurality being oriented such that the long axis liesperpendicular to a direction of travel, the lath brushes comprising aplurality of bristles being of sufficient number to support the washerhead frame against a front surface of the solar panel without damage tothe solar panel; and arranged within the washer head frame: a sprayermanifold assembly comprising: a gooseneck for receiving a connection toa flexible water hose; a sprayer manifold to receive a high-pressureflow of water from the gooseneck; at least one spray header to receivethe high-pressure flow of water from the sprayer manifold to supply thehigh-pressure flow to a plurality of nozzles configured to spray thefront face of the solar panel.
 16. The washer head frame of claim 15further comprising: a plurality of truck wheels rotatably fastened tothe washer head frame, the plurality of truck wheels being arranged tosupport the washer head frame when the washer head frame is oriented toa generally orthogonal orientation to a ground surface, the truck wheelsbeing configured to transport the washer head assembly over the groundsurface.
 17. The washer head frame of claim 15 further comprising: anupper trolley assembly comprising: a plurality of suspension wheels; anda plurality of upper lateral trolley wheels; and a lower trolleyassembly, comprising: a plurality of suspension wheels and a pluralityof lower lateral trolley wheels; and wherein the upper trolley assemblyand the lower trolley assembly held in parallel relationship one toanother by a plurality of connections to the washer head frame.
 18. Thewasher head assembly of claim 15, wherein: the upper trolley assemblyincludes an axial pivot allowing the upper lateral trolley assembly torotate axially to, alternately, engage or disengage upper lateraltrolley wheels with an upper edge of the solar panel.
 19. The washerhead assembly of claim 18 further comprising: a cam lever assemblycomprising a cam handle, a cam swivel and a backbone swivel cooperatingto rotate the upper trolley assembly to alternately engage or todisengage the upper lateral trolley wheels with the solar panel, the camlever assembly being configured to rotate the upper trolley assembly inresponse to.
 20. The washer head assembly of claim 18 furthercomprising: a spring arranged to urge cam lever assembly to rotate theupper trolley assembly to engage the upper lateral trolley wheels withthe solar panel.